An antenna device attached on a roof of a vehicle is applied to a wide variety of vehicles as an antenna device attached on a vehicle. The antenna device attached on the roof of the vehicle is required to have a design that does not impair the aesthetic appearance of the vehicle or a design that improves aerodynamic characteristics during running of the vehicle. The development of an antenna device called a shark fin antenna which is streamlined and becomes thinner toward the front of the vehicle is proceeding as the antenna device mentioned above. An antenna case of a shark fin antenna is formed from a resin material with high strength in order to suppress damage due to external pressure or impacts. However, since the roof of the vehicle is scratched when the antenna case and the roof of the vehicle come into contact with each other, a cover member is arranged between the antenna case and the roof of the vehicle (for example, Japanese Laid-Open Patent Publication No. 2014-33461). The cover member maintains a space between the antenna case and the roof of the vehicle and blinds a gap between the two.
However, in Japanese Laid-Open Patent. Publication No. 2014-33461, since a collar part 20b of an insulating base 20 is required to be screwed into a groove part 18a of a gap cover 18 when attaching the gap cover 18 to the insulating base 20, workability of the attachment is low. Furthermore, in Japanese Laid-Open Patent Publication No. 2014-33461, it was inconvenient that it cannot be confirmed visually or by touch that the groove part 18a is fitted into the collar part 20b. Both are welded together after the gap cover 18 is attached on the insulating base 20. In this state, since the gap cover 18 is in close contact with the antenna case 10 and the insulating base 20, it is difficult to detach the gap cover 18 from the insulating base 20 during maintenance, for example.